Method of polycarbonate preparation

ABSTRACT

Polycarbonates containing low or undetectable levels of Fries rearrangement product may be prepared by the melt reaction of a dihydroxy aromatic compound such as bisphenol A with an ester-substituted diaryl carbonate such as the diaryl carbonate of methyl salicylate, bis-methyl salicyl carbonate. Low levels of Fries product are obtained as the combined result of a highly effective catalyst system which suppresses the Fries reaction and the use of lower melt polymerization temperatures relative to temperatures required for the analogous polymerization reaction using diphenyl carbonate.

BACKGROUND OF THE INVENTION

This invention relates to the preparation of polycarbonates by the meltreaction of a bisphenol with an ester-substituted diaryl carbonate. Moreparticularly, the instant invention relates to the formation under mildconditions of polycarbonates having extremely low levels of Friesrearrangement products and possessing a high level of endcapping.

Polycarbonates, such as bisphenol A polycarbonate, are typicallyprepared either by interfacial or melt polymerization methods. Thereaction of a bisphenol such as bisphenol A (BPA) with phosgene in thepresence of water, a solvent such as methylene chloride , an acidacceptor such as sodium hydroxide and a phase transfer catalyst such astriethylamine is typical of the interfacial methodology. The reaction ofbisphenol A with a source of carbonate units such as diphenyl carbonateat high temperature in the presence of a catalyst such as sodiumhydroxide is typical of currently employed melt polymerization methods.Each method is practiced on a large scale commercially and each presentssignificant drawbacks.

The interfacial method for making polycarbonate has several inherentdisadvantages. First it is a disadvantage to operate a process whichrequires phosgene as a reactant due to obvious safety concerns. Secondit is a disadvantage to operate a process which requires using largeamounts of an organic solvent because expensive precautions must betaken to guard against any adverse environmental impact. Third, theinterfacial method requires a relatively large amount of equipment andcapital investment. Fourth, the polycarbonate produced by theinterfacial process is prone to having inconsistent color, higher levelsof particulates, and higher chloride content, which can cause corrosion.

The melt method, although obviating the need for phosgene or a solventsuch as methylene chloride requires high temperatures and relativelylong reaction times. As a result, by-products may be formed at hightemperature, such as the products arising by Fries rearrangement ofcarbonate units along the growing polymer chains. Fries rearrangementgives rise to undesired and uncontrolled polymer branching which maynegatively impact the polymer's flow properties and performance.

Some years ago, it was reported in U.S. Pat. No. 4,323,668 thatpolycarbonate could be formed under relatively mild conditions byreacting a bisphenol such as BPA with the diaryl carbonate formed byreaction phosgene with methyl salicylate. The method used relativelyhigh levels of transesterification catalysts such as lithium stearate inorder to achieve high molecular weight polycarbonate. High catalystloadings are particularly undesirable in melt polycarbonate reactionssince the catalyst remains in the product polycarbonate following thereaction. The presence of a transesterification catalyst in a thepolycarbonate may shorten the useful life span of articles madetherefrom by promoting increased water absorption, polymer degradationat high temperatures and discoloration.

It would be desirable, therefore, to minimize the amount of catalystrequired in the for the melt preparation of polycarbonate frombisphenols and ester substituted diaryl carbonates such as bis-methylsalicyl carbonate.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method for preparing polycarbonatecomprising heating a mixture comprising a catalyst; at least one diarylcarbonate having structure I

wherein R¹ and R² are independently C₁-C₂₀ alkyl radicals, C₄-C₂₀cycloalkyl radicals, or C₄-C₂₀ aromatic radicals, R³ and R⁴ areindependently at each occurrence a halogen atom, cyano group, nitrogroup, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, C₄-C₂₀ aromaticradical, C₁-C₂₀ alkoxy radical, C₄-C₂₀ cycloalkoxy radical, C₄-C₂₀aryloxy radical, C₁-C₂₀ alkylthio radical, C₄-C₂₀ cycloalkylthioradical, C₄-C₂₀ arylthio radical, C₁-C₂₀ alkylsulfinyl radical, C₄-C₂₀cycloalkylsulfinyl radical, C₄-C₂₀ arylsulfinyl radical, C₁-C₂₀alkylsulfonyl radical, C₄-C₂₀ cycloalkylsulfonyl radical, C₄-C₂₀arylsulfonyl radical, C₁-C₂₀ alkoxycarbonyl radical, C₄-C₂₀cycloalkoxycarbonyl radical, C₄-C₂₀ aryloxycarbonyl radical, C₂-C₆₀alkylamino radical, C₆-C₆₀ cycloalkylamino radical, C₅-C₆₀ arylaminoradical, C₁-C₄₀ alkylaminocarbonyl radical, C₄-C₄₀cycloalkylaminocarbonyl radical, C₄-C₄₀ arylaminocarbonyl radical, orC₁-C₂₀ acylamino radical; and b and c are independently integers 0-4;and at least one dihydroxy aromatic compound, said catalyst comprisingat least one source of alkaline earth ions or alkali metal ions, and atleast one quaternary ammonium compound, quaternary phosphonium compound,or a mixture thereof, said source of alkaline earth ions or alkali metalions being present in an amount such that between about 10⁻⁵ and about10⁻⁸ moles of alkaline earth metal ions or alkali metal ions are presentin the mixture relative per mole of dihydroxy aromatic compoundemployed, said quaternary ammonium compound, quaternary phosphoniumcompound or mixture thereof being present in an amount between about2.5×10⁻³ and about 1×10⁻⁶ moles per mole of dihydroxy aromatic compoundemployed.

The present invention further relates to a method for formingpolycarbonates by reaction of an ester-substituted diaryl carbonate inwhich the level of Fries rearrangement product in the productpolycarbonate is less than about 1000 parts per million (ppm) and thelevel of internal ester carbonate linkages in the product polycarbonateis less than about 1 percent of the total number of moles of dihydroxyaromatic compound employed and the level of terminal hydroxy estergroups in the product polycarbonate is less than about 1 percent of thetotal number of moles of dihydroxy aromatic compound employed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of preferred embodiments of the inventionand the examples included therein. In the following specification andthe claims which follow, reference will be made to a number of termswhich shall be defined to have the following meanings:

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

As used herein the term “polycarbonate” refers to polycarbonatesincorporating structural units derived from one or more dihydroxyaromatic compounds and includes copolycarbonates and polyestercarbonates.

As used herein, the term “melt polycarbonate” refers to a polycarbonatemade by the transesterification of a diaryl carbonate with a dihydroxyaromatic compound.

“BPA” is herein defined as bisphenol A or2,2-bis(4-hydroxyphenyl)propane.

“Catalyst system” as used herein refers to the catalyst or catalyststhat catalyze the transesterification of the bisphenol with the diarylcarbonate in the melt process.

The terms “bisphenol”, “diphenol” and “dihydric phenol” as used hereinare synonymous.

“Catalytically effective amount” refers to the amount of the catalyst atwhich catalytic performance is exhibited.

As used herein the term “Fries product” is defined as a structural unitof the product polycarbonate which upon hydrolysis of the productpolycarbonate affords a carboxy-substituted dihydroxy aromatic compoundbearing a carboxy group adjacent to one or both of the hydroxy groups ofsaid carboxy-substituted dihydroxy aromatic compound. For example, inbisphenol A polycarbonate prepared by a melt reaction method in whichFries reaction occurs, among the Fries products within the productpolycarbonate are those structural units, for example structure VIIIbelow, which afford 2-carboxy bisphenol A upon complete hydrolysis ofthe product polycarbonate.

The terms “Fries product” and “Fries group” are used interchangeablyherein.

The terms “Fries reaction” and “Fries rearrangement” are usedinterchangeably herein.

As used herein the term “aliphatic radical” refers to a radical having avalence of at least one comprising a linear or branched array of atomswhich is not cyclic. The array may include heteroatoms such as nitrogen,sulfur and oxygen or may be composed exclusively of carbon and hydrogen.Examples of aliphatic radicals include methyl, methylene, ethyl,ethylene, hexyl, hexamethylene and the like.

As used herein the term “aromatic radical” refers to a radical having avalence of at least one comprising at least one aromatic group. Examplesof aromatic radicals include phenyl, pyridyl, furanyl, thienyl,naphthyl, phenylene, and biphenyl. The term includes groups containingboth aromatic and aliphatic components, for example a benzyl group.

As used herein the term “cycloaliphatic radical” refers to a radicalhaving a valance of at least one comprising an array of atoms which iscyclic but which is not aromatic. The array may include heteroatoms suchas nitrogen, sulfur and oxygen or may be composed exclusively of carbonand hydrogen. Examples of cycloaliphatic radicals include cyclopropyl,cyclopentyl cyclohexyl, tetrahydrofuranyl and the like.

In the present invention it has been discovered that extremely lowlevels of catalyst may be employed to prepare polycarbonate using themelt reaction of an ester substituted diaryl carbonate with a bisphenol.The use of very low catalyst loadings is desirable from at least twoperspectives. First, the use of low catalyst levels during meltpolymerization tends to suppress the formation of undesired Friesrearrangement products. Second, because residual catalyst present in thepolymer tends to decrease the useful life span of articles made from itby increasing water absorption, decreasing thermal stability andpromoting discoloration, its minimization is desirable. Thepolycarbonate prepared by the method of the present invention is freeof, or contains undetectable levels of Fries rearrangement products.Moreover, in the absence of an added exogenous monofunctional phenol theproduct polycarbonate is very highly endcapped with less than 50% of theendgroups being free hydroxyl groups. Where an exogenous monofunctionalphenol is added to the polymerization mixture, high levels ofincorporation of said phenol are observed. In this manner both theidentity of the polymer endgroups and the polymer molecular weight maybe controlled in the melt reaction.

In the process of the present invention an ester-substituted diarylcarbonate having structure I is reacted under melt reaction conditionswith at least one dihydroxy aromatic compound in the presence of atleast one source of alkaline earth ions or alkali metal ions, and anorganic ammonium compound or an organic phosphonium compound or acombination thereof. Ester-substituted diaryl carbonates I areexemplified by bis-methyl salicyl carbonate (CAS Registry No.82091-12-1), bis-ethyl salicyl carbonate, bis-propyl salicyl carbonate,bis-butyl salicyl carbonate, bis-benzyl salicyl carbonate, bis-methyl4-chlorosalicyl carbonate and the like. Typically bis-methyl salicylcarbonate is preferred.

The dihydroxy aromatic compounds of the present invention are selectedfrom the group consisting of bisphenols having structure II,

wherein R⁵-R¹² are independently a hydrogen atom, halogen atom, nitrogroup, cyano group, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, orC₆-C₂₀ aryl radical; W is a bond, an oxygen atom, a sulfur atom, a SO₂group, a C₆-C₂₀ aromatic radical, a C₆-C₂₀ cycloaliphatic radical, orthe group

wherein R¹³ and R¹⁴ are independently a hydrogen atom, C₁-C₂₀ alkylradical, C₄-C₂₀ cycloalkyl radical, or C₄-C₂₀ aryl radical; or R¹³ andR¹⁴ together form a C₄-C₂₀ cycloaliphatic ring which is optionallysubstituted by one or more C₁-C₂₀ alkyl, C₆-C₂₀ aryl, C₅-C₂₁ aralkyl,C₅-C₂₀ cycloalkyl groups, or a combination thereof; dihydroxy benzeneshaving structure III

wherein R¹⁵ is independently at each occurrence a hydrogen atom, halogenatom, nitro group, cyano group, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkylradical, or C₄-C₂₀ aryl radical, d is an integer from 0 to 4; and

dihydroxy naphthalenes having structures IV and V

wherein R¹⁶, R¹⁷, R¹⁸ and R¹⁹ are independently at each occurrence ahydrogen atom, halogen atom, nitro group, cyano group, C₁-C₂₀ alkylradical, C₄-C₂₀ cycloalkyl radical, or C₄-C₂₀ aryl radical; e and f areintegers from 0 to 3, g is an integer from 0 to 4, and h is an integerfrom 0 to 2.

Suitable bisphenols II are illustrated by2,2-bis(4-hydroxyphenyl)propane (bisphenol A);2,2-bis(3-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-3-methylphenyl)propane;2,2-bis(4-hydroxy-3-isopropylphenyl)propane;2,2-bis(3-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-phenyl-4-hydroxyphenyl)propane;2,2-bis(3,5-dichloro-4-hydroxyphenyl)-propane;2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane;2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane;2,2-bis(3-chloro-4-hydroxy-5-methylphenyl)propane;2,2-bis(3-bromo-4-hydroxy-5-methylphenyl)propane;2,2-bis(3-chloro-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-bromo-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-chloro-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3,5-disopropyl-4-hydroxyphenyl)propane;2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3,5-diphenyl-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)propane;2,2-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)propane;2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dibromo-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-5-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)cyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dibromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;bis(3-chloro-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;4,4′dihydroxy-1,1-biphenyl; 4,4′-dihydroxy-3,3′-dimethyl-1,1-biphenyl;4,4′-dihydroxy-3,3′-dioctyl-1,1-biphenyl; 4,4′-dihydroxydiphenylether;4,4′-dihydroxydiphenylthioether;1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene;1,3-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene;1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene and1,4-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene.

Suitable dihydroxy benzenes III are illustrated by hydroquinone,resorcinol, methylhydroquinone, phenylhydroquinone, 4-phenylresorcinoland 4-methylresorcinol.

Suitable dihydroxy naphthalenes IV are illustrated by 2,6-dihydroxynaphthalene; 2,6-dihydroxy-3-methyl naphthalene; and2,6-dihydroxy-3-phenyl naphthalene.

Suitable dihydroxy naphthalenes V are illustrated by 1,4-dihydroxynaphthalene; 1,4-dihydroxy-2-methyl naphthalene; 1,4-dihydroxy-2-phenylnaphthalene and 1,3-dihydroxy naphthalene.

The catalyst used in the method of the present invention comprises atleast one source of alkaline earth ions or alkali metal ions, and atleast one quaternary ammonium compound, quaternary phosphonium compoundor a mixture thereof, said source of alkaline earth ions or alkali metalions being used in an amount such that the amount of alkaline earth oralkali metal ions present in the reaction mixture is in a range betweenabout 10⁻⁵ and about 10⁻⁸ moles alkaline earth or alkali metal ion permole of dihydroxy aromatic compound employed.

The quaternary ammonium compound is selected from the group of organicammonium compounds having structure VI

wherein R²⁰-R²³ are independently a C₁-C₂₀ alkyl radical, C₄-C₂₀cycloalkyl radical, or a C₄-C₂₀ aryl radical; and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isselected from the group consisting of hydroxide, halide, carboxylate,sulfonate, sulfate, formate, carbonate, and bicarbonate.

Suitable organic ammonium compounds comprising structure VI areillustrated by tetramethyl ammonium hydroxide, tetrabutyl ammoniumhydroxide, tetramethyl ammonium acetate, tetramethyl ammonium formateand tetrabutyl ammonium acetate.

The quaternary phosphonium compound is selected from the group oforganic phosphonium compounds having structure VII

wherein R²⁴-R²⁷ are independently a C₁-C₂₀ alkyl radical, C₄-C₂₀cycloalkyl radical, or a C₄-C₂₀ aryl radical; and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isan anion selected from the group consisting of hydroxide, halide,carboxylate, sulfonate, sulfate, formate, carbonate, and bicarbonate.Suitable organic phosphonium compounds comprising structure VII areillustrated by tetramethyl phosphonium hydroxide, tetramethylphosphonium acetate, tetramethyl phosphonium formate, tetrabutylphosphonium hydroxide, and tetrabutyl phosphonium acetate.

Where X⁻ is a polyvalent anion such as carbonate or sulfate it isunderstood that the positive and negative charges in structures VI andVII are properly balanced. For example, where R²⁰-R²³ in structure VIare each methyl groups and X⁻ is carbonate, it is understood that X⁻represents ½ (CO₃ ⁻²).

Suitable sources of alkaline earth ions include alkaline earthhydroxides such as magnesium hydroxide and calcium hydroxide. Suitablesources of alkali metal ions include the alkali metal hydroxidesillustrated by lithium hydroxide, sodium hydroxide and potassiumhydroxide. Other sources of alkaline earth and alkali metal ions includesalts of carboxylic acids, such as sodium acetate and derivatives ofethylene diamine tetraacetic acid (EDTA) such as EDTA tetrasodium salt,and EDTA magnesium disodium salt.

In the method of the present invention an ester-substituted diarylcarbonate I, at least one dihydroxy aromatic compound and a catalyst arecontacted in a reactor suitable for conducting melt polymerization. Therelative amounts of ester-substituted diaryl carbonate and dihydroxyaromatic compound are such that the molar ratio of carbonate I todihydroxy aromatic compound is in a range between about 1.20 and about0.8, preferably between about 1.10 and about 0.9 and still morepreferably between about 1.05 and about 1.01.

The amount of catalyst employed is such that the amount of alkalineearth metal ion or alkali metal ions present in the reaction mixture isin a range between about 1×10⁻⁵ and about 1×10⁻⁸, preferably betweenabout 5×10⁻⁵ and about 1×10⁻⁷, and still more preferably between about5×10⁻⁵ and about 5×10⁻⁷ moles of alkaline earth metal ion or alkalimetal ion per mole dihydroxy aromatic compound employed. The quaternaryammonium compound, quaternary phosphonium compound or a mixture thereofis used in an amount corresponding to about 2.5×10⁻³ and 1×10⁻⁶ molesper mole dihydroxy aromatic compound employed.

Typically the ester-substituted diaryl carbonate, at least one dihydroxyaromatic compound and the catalyst are combined in a reactor which hasbeen treated to remove adventitious contaminants capable of catalyzingboth the transesterification and Fries reactions observed inuncontrolled melt polymerizations of diaryl carbonates with dihydroxyaromatic compounds. Contaminants such as sodium ion adhering to thewalls of a glass lined reactor are typical and may be removed by soakingthe reactor in mild acid, for example 3 normal hydrochloric acid,followed by removal of the acid and soaking the reactor in high puritywater, such as deionized water.

In one embodiment of the present invention an ester-substituted diarylcarbonate, such as bis-methyl salicyl carbonate, at least one dihydroxyaromatic compound, such as BPA, and a catalyst comprising alkali metalions, such as sodium hydroxide, and a quaternary ammonium compound, suchas tetramethyl ammonium hydroxide, or a quaternary phosphonium compound,such as tetrabutyl phosphonium acetate, are charged to a reactor and thereactor is purged with an inert gas such as nitrogen or helium. Thereactor is then heated to a temperature in a range between about 100° C.and about 340° C., preferably between about 100° C. and about 280° C.,and still more preferably between about 140° C. and about 240° C. for aperiod of from about 0.25 to about 5 hours, preferably from about 0.25to about 2 hours, and still more preferably from about 0.25 hours toabout 1.25 hours. While the reaction mixture is heated the pressure overthe reaction mixture is gradually reduced from ambient pressure to afinal pressure in a range between about 0.001 mmHg and about 400 mmHg,preferably 0.01 mmHg and about 100 mmHg, and still more preferably about0.1 mmHg and about 10 mmHg.

Control of the pressure over the reaction mixture allows the orderlyremoval of the phenolic by-product formed when the dihydroxy aromaticcompound undergoes a transesterification reaction with a species capableof releasing a phenolic by-product, for example bis-methyl salicylcarbonate or a growing polymer chain endcapped by a methyl salicylgroup. As noted above the reaction may be conducted at subambientpressure. In an alternate embodiment of the present invention thereaction may be conducted at slightly elevated pressure, for example apressure in a range between about 1 and about 2 atmospheres.

As noted, the use of excessive amounts of catalyst may affect negativelythe structure and properties of a polycarbonate prepared under meltpolymerization conditions. The present invention provides a method ofmelt polymerization employing a highly effective catalyst systemcomprising at least one source of alkaline earth or alkali metal ions,and a quaternary ammonium compound or quaternary phosphonium compound ormixture thereof which provides useful reaction rates at very lowcatalyst concentrations, thereby minimizing the amount of residualcatalyst remaining in the product polycarbonate. Limiting the amount ofcatalyst employed according to the method of the present inventionprovides a new and useful means of controlling the structural integrityof the product polycarbonate as well. Thus, the method of the presentinvention provides a product polycarbonate having a weight averagemolecular weight, as determined by gel permeation chromatography, in arange between about 10,000 and about 100,000 Daltons, preferably betweenabout 15,000 and about 60,000 Daltons, and still more preferably betweenabout 15,000 and about 50,000 Daltons said product polycarbonate havingless than about 1000, preferably less than about 500, and still morepreferably less than about 100 parts per million (ppm) Fries product.Structure VIII below

illustrates the Fries product structure present in a polycarbonateprepared from bisphenol A. As indicated, the Fries product may serve asa site for polymer branching, the wavy lines indicating polymer chainstructure.

In addition to providing a product polycarbonate containing only verylow levels of Fries products, the method of the present inventionprovides polycarbonates containing very low levels of other undesirablestructural features which arise from side reactions taking place duringmelt the polymerization reaction between ester-substituted diarylcarbonates I and dihydroxy aromatic compounds. One such undesirablestructural feature has structure IX

and is termed an internal ester-carbonate linkage. Structure IX isthought to arise by reaction of an ester-substituted phenol by-product,for example methyl salicylate, at its ester carbonyl group with adihydroxy aromatic compound or a hydroxy group of a growing polymerchain. Further reaction of the ester-substituted phenolic hydroxy groupleads to formation of a carbonate linkage. Thus, the ester-substitutedphenol by-product of reaction of an ester-substituted diaryl carbonatewith a dihydroxy aromatic compound, may be incorporated into the mainchain of a linear polycarbonate. The presence of uncontrolled amounts ofester carbonate linkages in the polycarbonate polymer chain isundesirable.

Another undesirable structural feature present in melt polymerizationreactions between ester-substituted diaryl carbonates and dihydroxyaromatic compounds is the ester-linked terminal group having structure X

which possesses a free hydroxyl group. Structure X is thought to arisein the same manner as structure IX but without further reaction of theester-substituted phenolic hydroxy group. The presence of uncontrolledamounts of hydroxy terminated groups such as X is undesirable. Instructures VIII, IX and X the wavy line shown as

represents the product polycarbonate polymer chain structure.

The present invention, in sharp contrast to known methods of effectingthe melt polymerization of an ester-substituted diaryl carbonate and adihydroxy aromatic compound, provides a means of limiting the formationof internal ester-carbonate linkages having structure IX as well asester-linked terminal groups having structure X, during meltpolymerization. Thus in a product polycarbonate prepared using themethod of the present invention structures, IX and X, when present,represents less than 1 mole percent of the total amount of allstructural units present in the product polymer derived from dihydroxyaromatic compounds employed as starting materials for the polymersynthesis.

An additional advantage of the method of the present invention overearlier methods of melt polymerization of ester-substituted diarylcarbonates and dihydroxy aromatic compounds, derives from the fact thatthe product polymer is endcapped with ester-substituted phenoxyendgroups and contains very low levels, less than about 50 percent,preferably less than about 10 percent, and still more preferably lessthan about 1 percent, of polymer chain ends bearing free hydroxy groups.The ester substituted terminal groups are sufficiently reactive to allowtheir displacement by other phenols such as p-cumylphenol. Thus,following the melt polymerization the product polycarbonate may betreated with one or more exogenous phenols to afford a polycarbonateincorporating endgroups derived from the exogenous phenol. The reactionof the ester substituted terminal groups with the exogenous phenol maybe carried out in a first formed polymer melt or in a separate step.

In one embodiment of the present invention an exogenous monofunctionalphenol, for example p-cumylphenol, is added at the outset of thereaction between the ester substituted diaryl carbonate and thedihydroxy aromatic compound. The product polycarbonate then containsendgroups derived from the exogenous monofunctional phenol. Theexogenous monofunctional phenol serves both to control the molecularweight of the product polycarbonate and to determine the identity of thepolymer endgroups. The exogenous monofunctional phenol may be added inamounts ranging from about 0.1 to about 10 mole percent, preferably fromabout 0.5 to about 8 mole percent and still more preferably from about 1to about 6 mole percent based on the total number of moles ofdihydroxyaromatic compound employed in the polymerization. Additionalcatalyst is not required apart from the catalytically effective amountadded to effect the polymerization reaction. Suitable exogenousmonofunctional phenols are exemplified by p-cumylphenol; 2,6-xylenol;4-t-butylphenol; p-cresol; 1-naphthol; 2-naphthol; cardanol;3,5-di-t-butylphenol, p-nonylphenol; p-octadecylphenol; and phenol. Inalternative embodiments of the present invention the exogenousmonofunctional phenol may be added at an intermediate stage of thepolymerization or after its completion. In such alternative embodimentsthe exogenous phenol may exert a controlling effect upon the molecularweight of the product polycarbonate and will control the identity of thepolymer terminal groups.

The present invention may be used to prepare polycarbonate productshaving very low levels (less than 1 ppm) of trace contaminants such asiron, chloride ion, and sodium ion. Where such extremely low levels oftrace contaminants is desired it is sufficient to practice the inventionusing starting materials, ester-substituted diary carbonate anddihydroxy aromatic compound having correspondingly low levels of thetrace contaminants in question. For example, the preparation bisphenol Apolycarbonate containing less than 1 ppm each of iron, chloride ion andsodium ion may be made by the method of the present invention usingstarting materials bis-methyl salicyl carbonate and bisphenol Acontaining less than 1 ppm iron, chloride ion and sodium ion.

The method of the present invention can be conducted as a batch or acontinuous process. Any desired apparatus can be used for the reaction.The material and the structure of the reactor used in the presentinvention is not particularly limited as long as the reactor has anordinary capability of stirring and the presence of adventitiouscatalysts can be controlled. It is preferable that the reactor iscapable of stirring in high viscosity conditions as the viscosity of thereaction system is increased in later stages of the reaction.

Polycarbonates prepared using the method of the present invention may beblended with conventional additives such as heat stabilizers, moldrelease agents and UV stabilizers and molded into various moldedarticles such as optical disks, optical lenses, automobile lampcomponents and the like. Further, the polycarbonates prepared using themethod of the present invention may be blended with other polymericmaterials, for example, other polycarbonates, polyestercarbonates,polyesters and olefin polymers such as ABS.

EXAMPLES

The following examples are set forth to provide those of ordinary skillin the art with a detailed description of how the methods claimed hereinare evaluated, and are not intended to limit the scope of what theinventors regard as their invention. Unless indicated otherwise, partsare by weight, temperature is in ° C.

Molecular weights are reported as number average (M_(n)) or weightaverage (M_(w)) molecular weight and were determined by gel permeationchromatography (GPC) analysis, using a polycarbonate molecular weightstandard to construct a broad standard calibration curve against whichpolymer molecular weights were determined. The temperature of the gelpermeation columns was about 25° C. and the mobile phase was chloroform.

Fries content was measured by the KOH methanolysis of resin and isreported as parts per million (ppm). The Fries content for each of themelt polycarbonates listed in Table 1 was determined as follows. First,0.50 grams of polycarbonate was dissolved in 4.0 ml of THF (containingp-terphenyl as internal standard). Next, 3.0 ml of 18% KOH in methanolwas added to this solution. The resulting mixture was stirred for twohours at this temperature. Next, 1.0 ml of acetic acid was added, andthe mixture was stirred for 5 minutes. Potassium acetate by-product wasallowed to crystallize over 1 hour. The solid was filtered off and theresulting filtrate was analyzed by liquid chromoatograph usingp-terphenyl as the internal standard.

Internal ester-carbonate and terminal hydroxy-ester groups were measuredby ¹³C- and ³¹P-NMR respectively. Terminal hydroxy ester groups werefirst derivatized with 2-chloro-1,3,2-dioxaphopholane (Aldrich).

Melt polymerization reactions were run in a 100 mL glass reactor adaptedfor distillation under vacuum equipped with a solid nickel helicalagitator. The reactor was configured such that by-product phenol ormethyl salicylate could be distilled out of the reaction vessel andcondensed in a chilled receiving vessel. Prior to its use, the reactorwas soaked in 3N HCl for a period of 12 hours and was then soaked for anadditional 12 hours in deionized water (18-Mohm) and placed in a dryingoven overnight. Reaction temperature was controlled by immersion of thereactor into a fluidized sand bath equipped with a PID temperaturecontroller. The temperature of the sand bath was monitored at thereactor sand bath interface. The pressure of the reaction vessel wascontrolled by means of a vacuum pump coupled to a nitrogen bleed. Thepressure within the reactor was measured with an MKS pirani gauge.Sodium hydroxide (J. T. Baker, 1×10⁻⁶ mole per mole bisphenol A) andtetramethyl ammonium hydroxide (Sachem, 2.5×10⁻⁴ mole per mole bisphenolA) or tetrabutyl phosphonium acetate (Sachem, 2.5×10⁻⁴ mole per molebisphenol A) were added as solutions in deionized (18 Mohm) water. Wherethe catalyst level was varied, the concentration of the catalystsolution was adjusted such that the volume of water introduced in thecatalyst introduction step was held constant.

Examples 1-3 and Comparative Examples 1-4

The reactor was charged at ambient temperature and pressure with solidbisphenol A (General Electric Plastics Japan Ltd., 0.08761 mol) andsolid bis-methyl salicyl carbonate (0.0880-0.0916 mol) or solid diphenylcarbonate (General Electric Plastics Japan Ltd., 0.0946 mol). In someinstances a monofunctional phenol such as p-cumylphenol (0.0027-0.0088mol) was added in order to limit the molecular weight of the polymer andcontrol chain endgroup identity. The catalyst was then injected into thebisphenol A layer and the reactor was assembled. The reactor was thenevacuated briefly and nitrogen was reintroduced. This step was repeatedthree times. The reactor was then lowered into the sand bath maintainedat 180° C. After a five minute period stirring at 250 rpm was initiated.After a total of 10 minutes the reaction mixture had fully melted. Thetemperature of the bath was raised to 210° C. over a five minute period.The pressure in the reactor was then reduced to 180 mmHg at which pointthe phenolic by-product began to distill from the reaction vessel intothe receiving vessel. The reaction mixture was held at 210° C. and 180mmHg for 20 minutes. The pressure was then lowered to 100 mmHg stirredfor an additional 20 minutes after which time the temperature was raisedto 240 ° C. over a five minute period. The pressure was then lowered to15 mmHg and the reaction mixture was stirred at 240° C. at 15 mmHg for20 minutes. The temperature was then raised to 270° C. over a fiveminute period and the pressure was then lowered to 2 mmHg. The reactionmixture was stirred at 270° C. at 2 mmHg for 10 minutes. The temperaturewas then raised to 310° C. over a ten minute period and the pressure waslowered to 1.1 mmHg. The reaction mixture was stirred at 310° C. at 1.1mmHg for 30 minutes after which the reaction vessel was raised from thesand bath and the molten product polymer was scooped from the reactionvessel into a liquid nitrogen bath in order to quench the reaction.

Data for Examples 1-3 and Comparative Examples 1-5 are gathered in Table1 and illustrate the utility of the method of the present invention. Inthe Comparative Examples 1-5 and Examples 1-3 no p-cumylphenol was addedas a chainstopper. The column heading “DAC” indicates which diarylcarbonate was employed. “DPC” is diphenyl carbonate used inComparative-Example 1 (CE-1). “BMS” is bis-methyl salicyl carbonate. Theratio “DAC/BPA” represents the initial molar ratio of diaryl carbonateto bisphenol A employed in the reaction. “M_(n)” represents numberaverage molecular weight of the product polymer. “Fries level” indicatesthe concentration of Fries rearrangement product present in the productpolymer. Fries levels were determined by complete solvolysis (KOHcatalyzed methanolysis) of the product polymer and quantitativemeasurement of the amount of Fries product, 2-carboxybisphenol A (CASNo. 101949-49-9), present by HPLC. “EC (%)” represents the percentage ofpolymer chain ends not terminating in a hydroxyl group. Hydroxylendgroup concentrations were determined by quantitative infraredspectroscopy. Phenol and salicyl endgroups were determined by HPLCanalysis after product solvolysis.

TABLE 1 REACTION OF BPA WITH DIARYLCARBONATE (DAC) Example DAC DAC/BPAM_(n) Fries level EC (%) CE-1 DPC 1.08 6250 946 41% Example 1 BMSC 1.084293 not detected >99%   Example 2 BMSC 1.04 8499 not detected >99%  Example 3 BMSC 1.02 13762 not detected 98% CE-2¹ BMSC 1.04 7683 43 CE-3²BMSC 1.04 7892 282 CE-4³ BMSC 1.04 gel 8502 CE-5³ BMSC 1.0  5910 98 47%¹Catalyst was NaOH at 1 × 10⁻⁶ mole per mole BPA ²Catalyst wastetrabutylphosphonium acetate at 2.5 × 10⁻⁴ mole per mole BPA ³Catalystwas lithium stearate at 1 × 10⁻³ moles per mole BPA

Comparative Example 1 highlights differences between melt polymerizationbehavior of DPC and BMSC in reactions with bisphenol A. Meltpolymerization using BMSC (Example 1) affords an undetectable level ofFries product and a very high level of endcapping, whereas meltpolymerization using DPC under the same conditions using the samecatalyst as that used in Example 1 leads to a high level (946 ppm) ofFries product and a far lower endcapping level. Examples 1-3 illustratethe melt polymerization of BMSC with BPA according to the method of thepresent invention which affords polycarbonate containing undetectablelevels of Fries product and very high endcapping levels.

According to the method of the present invention the catalyst comprisesat least one source of alkaline earth ions or alkali metal ions, and atleast one quaternary ammonium compound, quaternary phosphonium compoundor a mixture thereof. Comparative Examples 2 and 3 illustrate thisrequirement. In Comparative Example 2, a source of alkali metal ions,NaOH, was present but no quaternary ammonium compound or quaternaryphosphonium compound was present. In Comparative Example, 3 a quaternaryphosphonium compound, tetra butyl phosphonium acetate, was present butno source of alkali metal ions was present. In both instances detectablelevels of Fries product were observed.

The data in Table 1 further illustrate the superiority of the method ofthe present invention over earlier polymerization methods using BMSC.Comparative Examples 4 and 5 show the effect of using lithium stearateat a level (1×10⁻³ mole per mole BPA) taught by U.S. Pat. No. 4,323,668.Comparative Example 4 was run using the protocol used in Examples 1-3and the product polycarbonate showed such a high level of Fries productthat its molecular weight could not be determined due to the very highlevel of branching which occurred. The product polycarbonate wasrecovered as a gel which could not be dissolved for gel permeationchromatography. Comparative Example 5 was run under a milder temperatureregime, the maximum temperature was 260° C. (See below), than that usedin Examples 1-3 and Comparative Examples 1-4, yet nonetheless theproduct polymer contained a significant amount of Fries product, 98 ppm.

Comparative Example No. 5

(CE-5, Table 1)

The reactor, equipped and passivated as described above, was charged atambient temperature and pressure with solid bisphenol A (GeneralElectric Plastics Japan Ltd., 0.100 mol) and solid bis-methyl salicylcarbonate (0.100 mol). Lithium stearate catalyst (Kodak, 1×10⁻³ mole permole bisphenol A) was added as a solid and the reactor was assembled.The reactor was then evacuated briefly and nitrogen was reintroduced.The degassing step was repeated three times. The reactor was thenlowered into the sand bath maintained at 150° C. After a five minuteperiod stirring at 250 rpm was initiated. These conditions weremaintained for 60 minutes. The temperature of the bath was then raisedto 260° C. The pressure in the reactor was then reduced to 10 mmHg atwhich point the methyl salicylate by-product began to distill from thereaction vessel into the receiving vessel. The reaction mixture was heldat 260° C. and 10 mmHg for 10 minutes after which the reaction vesselwas raised from the sand bath and the molten product polymer was scoopedfrom the reaction vessel into a liquid nitrogen bath in order to quenchthe reaction. The product polycarbonate was characterized by gelpermeation chromatography and found to have M_(w)=14353 and M_(n)=5910.The level of Fries product was determined to be 98 ppm.

As noted, it has been found that the inclusion of an exogenous phenolsuch as p-cumylphenol in the melt reaction of a bisphenol with anester-substituted diaryl carbonate according to the method of thepresent invention affords polycarbonate containing p-cumylphenolendgroups. Data are gathered in Table 2 which demonstrate the surprisingefficiency of this transformation relative to the analogous reactionusing diphenyl carbonate (DPC). Comparative Example 7 illustrates thelow levels of PCP incorporation in the product polycarbonate encounteredwhen a mixture of a bisphenol, DPC and an endcapping agent,p-cumylphenol (PCP) are reacted in the melt. Conversely, Example 5conducted utilizing the method of the present invention reveals a highlevel of PCP incorporation. In the polycarbonate product formed inComparative Example 7 roughly half of the endgroups were found by NMR tobe derived from PCP and half derived from phenol.

TABLE 2 REACTION OF BPA WITH DAC IN THE PRESENCE OF PCP Example DACDAC/BPA PCP M_(n) EC (%) % PCP CE-6 DPC 1.08 — 6250 41% — CE-7 DPC 1.083.05 5674 60% 25% Example 4 BMSC 1.04 — 8499 100%  — Example 5 BMSC 1.035.07 9744 99% 97%

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood by thoseskilled in the art that variations and modifications can be effectedwithin the spirit and scope of the invention.

What is claimed is:
 1. A method of preparing polycarbonate comprisingheating a mixture comprising a catalyst; at least one diaryl carbonatehaving structure I

wherein R¹ and R² are independently C₁-C₂₀ alkyl radicals, C₄-C₂₀cycloalkyl radicals, or C₄-C₂₀ aromatic radicals, R³ and R⁴ areindependently at each occurrence a halogen atom, cyano group, nitrogroup, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, C₄-C₂₀ aromaticradical, C₁-C₂₀ alkoxy radical, C₄-C₂₀ cycloalkoxy radical, C₄-C₂₀aryloxy radical, C₁-C₂₀ alkylthio radical, C₄-C₂₀ cycloalkylthioradical, C₄-C₂₀ arylthio radical, C₁-C₂₀ alkylsulfinyl radical, C₄-C₂₀cycloalkylsulfinyl radical, C₄-C₂₀ arylsulfinyl radical, C₁-C₂₀alkylsulfonyl radical, C₄-C₂₀ cycloalkylsulfonyl radical, C₄-C₂₀arylsulfonyl radical, C₁-C₂₀ alkoxycarbonyl radical, C₄-C₂₀cycloalkoxycarbonyl radical, C₄-C₂₀ aryloxycarbonyl radical, C₂-C₆₀alkylamino radical, C₆-C₆₀ cycloalkylamino radical, C₅-C₆₀ arylaminoradical, C₁-C₄₀ alkylaminocarbonyl radical, C₄-C₄₀cycloalkylaminocarbonyl radical, C₄-C₄₀ arylaminocarbonyl radical, orC₁-C₂₀ acylamino radical; and b and c are independently integers 0-4;and at least one dihydroxy aromatic compound; said catalyst comprisingat least one source of alkaline earth ions or alkali metal ions, and atleast one quaternary ammonium compound, quaternary phosphonium compound,or a mixture thereof, said source of alkaline earth ions or alkali metalions being present in an amount such that between about 10⁻⁵ and about10⁻⁸ moles of alkaline earth metal ions or alkali metal ions are presentin the mixture per mole of dihydroxy aromatic compound employed, saidquaternary ammonium compound, quaternary phosphonium compound or mixturethereof being present in an amount between about 2.5×10⁻³ and about1×10⁻⁶ moles per mole of dihydroxy aromatic compound employed.
 2. Amethod according to claim 1 wherein said dihydroxy aromatic compoundselected from the group consisting of bisphenols having structure II,

wherein R⁵-R¹² are independently a hydrogen atom, halogen atom, nitrogroup, cyano group, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, orC₆-C₂₀ aryl radical; W is a bond, an oxygen atom, a sulfur atom, a SO₂group, a C₆-C₂₀ aromatic radical, a C₆-C₂₀ cycloaliphatic radical, orthe group

wherein R¹³ and R¹⁴ are independently a hydrogen atom, C₁₋C₂₀ alkylradical, C₄-C₂₀ cycloalkyl radical, or C₄-C₂₀ aryl radical; or R¹³ andR¹⁴ together form a C₄-C₂₀ cycloaliphatic ring which is optionallysubstituted by one or more C₁-C₂₀ alkyl, C₆-C₂₀ aryl, C₅-C₂₁ aralkyl,C₅-C₂₀ cycloalkyl groups, or a combination thereof; dihydroxy benzeneshaving structure III

wherein R¹⁵ is independently at each occurrence a halogen atom, nitrogroup, cyano group, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, ora C₄-C₂₀ aryl radical; d is an integer from 0 to 4; and dihydroxynaphthalenes having structures IV and V

wherein R¹⁶, R¹⁷, R¹⁸ and R¹⁹ are independently at each occurrence ahalogen atom, nitro group, cyano group, C₁-C₂₀ alkyl radical, C₄-C₂₀cycloalkyl radical, or C₄-C₂₀ aryl radical; e and f are integers from 0to 3, g is an integer from 0 to 4, and h is an integer from 0 to
 2. 3. Amethod according to claim 1 wherein said quaternary ammonium compoundcomprises structure VI

wherein R²⁰-R²³ are independently a C₁-C₂₀ alkyl radical, C₄-C₂₀cycloalkyl radical, or a C₄-C₂₀ aryl radical; and X⁻ is an organic orinorganic anion.
 4. A method according to claim 3 wherein R²⁰-R²³ areindependently C₁-C₅ alkyl.
 5. A method according to claim 4 whereinR²⁰-R²³ are each methyl radicals.
 6. A method according to claim 2wherein said anion is selected from the group consisting of hydroxide,halide, carboxylate, sulfonate, sulfate, carbonate, and bicarbonate. 7.A method according to claim 1 wherein said quaternary ammonium compoundis tetramethyl ammonium hydroxide.
 8. A method according to claim 1wherein said phosphonium compound comprises structure VII

wherein R²⁴-R²⁷ are independently a C₁-C₂₀ alkyl radical, C₄-C₂₀cycloalkyl radical, or a C₄-C₂₀ aryl radical; and X⁻ is an organic orinorganic anion.
 9. A method according to claim 8 wherein R²⁴-R²⁷ areindependently C₁-C₅ alkyl.
 10. A method according to claim 9 whereinR²⁴-R²⁷ are each methyl radicals.
 11. A method according to claim 8wherein said anion is selected from the group consisting of hydroxide,halide, carboxylate, sulfonate, sulfate, carbonate, and bicarbonate. 12.A method according to claim 1 wherein said quaternary phosphoniumcompound is tetrabutyl phosphonium hydroxide.
 13. A method according toclaim 1 wherein said source of alkaline earth or alkali metal ions is analkali metal hydroxide, an alkaline earth metal hydroxide or a mixturethereof.
 14. A method according to claim 13 wherein said alkali metalhydroxide is lithium hydroxide, sodium hydroxide, potassium hydroxide ora mixture thereof.
 15. A method according to claim 1 wherein said sourceof alkaline earth or alkali metal ions is a salt of EDTA.
 16. A methodaccording to claim 15 wherein said salt of EDTA is EDTA magnesiumdisodium salt.
 17. A method according to claim 1 wherein said mixture isheated to a temperature in a range between about 100° C. and about 340°C.
 18. A method according to claim 17 wherein said mixture is heated toa temperature in a range between about 100° C. and about 280° C.
 19. Amethod according to claim 18 wherein said mixture is heated to atemperature in a range between about 140° C. and about 240° C.
 20. Amethod according to claim 1 wherein said mixture is heated at subambientpressure.
 21. A method according to claim 20 wherein said pressure is ina range between about 0.00001 and about 0.9 atmospheres.
 22. A methodaccording to claim 1 wherein said mixture is heated at ambient orsuprambient pressure.
 23. A method according to claim 22 wherein saidpressure is in a range between about 1 and about 2 atmospheres.
 24. Amethod according to claim 1 wherein diaryl carbonate 1 is bis-methylsalicyl carbonate.
 25. A method according to claim 24 wherein the endgroups are derived from methyl salicylate.
 26. A method according toclaim 2 wherein bisphenol II is selected from the group consisting of2,2-bis(4-hydroxyphenyl)propane (bisphenol-A);bis(4-hydroxy-3-methylphenyl)cyclohexane;2,2-bis(4-hydroxy-3-methylphenyl)propane; bis(4-hydroxyphenyl)methane;1,1-bis(4-hydroxyphenyl)ethane; 2,2-bis(4-hydroxyphenyl)butane;2,2-bis(4-hydroxyphenyl)octane;2,2-bis(4-hydroxy-3-tert-butylphenyl)propane;1,1-bis(4-hydroxy-3-sec-butylphenyl)propane;2,2-bis(4-hydroxy-3-bromophenyl)propane;1,1-bis(4-hydroxyphenyl)cyclopentane;1,1-bis(4-hydroxyphenyl)cyclohexane; and 4,4′-dihydroxydiphenyl ether.27. A method according to claim 26 wherein bisphenol II is bisphenol A.28. A method according to claim 1, said mixture further comprising atleast one exogenous monofunctional phenol.
 29. A method according toclaim 28 wherein said polycarbonate comprises endgroups derived from anexogenous monofunctional phenol.
 30. A method according to claim 29wherein said end groups are derived from said monofunctional phenolsselected from the group consisting of 2,6-xylenol, p-t-butylphenol,p-cresol, cardanol, p-cumylphenol, p-nonylphenol, p-octadecylphenol,1-naphthol, and 2-naphthol.
 31. A method according to claim 1 whereinsaid dihydroxy aromatic compound contains less than 1.0 parts permillion each of sodium ion, iron and chloride.
 32. A method according toclaim 1 wherein said polycarbonate contains less than 1.0 parts permillion each of sodium ion, iron and chloride.
 33. A molded articleprepared from the polycarbonate made by the method of claim
 32. 34. Amethod of preparing bisphenol A polycarbonate comprising heating amixture of bisphenol A with from about 0.8 to about 1.10 molarequivalents of bis-methyl salicyl carbonate at a temperature in a rangebetween about 140° C. and about 240° C., and a pressure in a rangebetween about 0.01 mmHg and about 760 mmHg, in the presence of acatalyst comprising sodium hydroxide and a quaternary ammonium compoundor quaternary phosphonium compound, said sodium hydroxide being presentin an amount in a range between about 1×10⁻⁵ and about 1×10⁻⁸ molessodium hydroxide per mole starting bisphenol A, said quaternary ammoniumcompound or quaternary phosphonium compound being present in an amountbetween about 2.5×10⁻³ and about 2.5×10⁻⁶ moles per mole startingbisphenol A.
 35. A method according to claim 34 wherein the quaternaryammonium compound is tetramethyl ammonium hydroxide.
 36. A methodaccording to claim 34 wherein the quaternary phosphonium compound istetrabutyl phosphonium acetate.
 37. A method of preparing bisphenol Apolycarbonate comprising heating a mixture of bisphenol A with fromabout 0.8 to about 1.10 molar equivalents, based on moles of bisphenolA, of bis-methyl salicyl carbonate, and about 0.1 mole percent to 10mole percent based upon the number of moles of bisphenol A employed, ofa monofunctional phenol, at a temperature in a range between about 140°C. and about 240° C., and a pressure in a range between about 0.01 mmHgand about 760 mmHg, in the presence of a catalyst comprising sodiumhydroxide and a quaternary ammonium compound or quaternary phosphoniumcompound, said sodium hydroxide being present in an amount in a rangebetween about 1×10⁻⁵ and about 1×10⁻⁸ moles sodium hydroxide per molestarting bisphenol A, said quaternary ammonium compound or quaternaryphosphonium compound being present in an amount between about 2.5×10⁻³and about 2.5×10⁻⁶ moles per mole starting bisphenol A.
 38. A methodaccording to claim 35 in which the monofunctional phenol is selectedfrom the group comprising 2,6-xylenol, p-t-butylphenol, p-cresol,cardanol, p-cumylphenol, p-nonylphenol, p-octadecylphenol, 1-naphthol,and 2-naphthol.